The present invention relates to a method of starting up a water-cooled nuclear reactor, and more particularly to a method of starting up a boiling water reactor.
In a power plant including a water-cooled nuclear reactor, particularly, a boiling water reactor, it has been known that the concentrations of the oxidating substances, such as oxygen and hydrogen peroxide, in a cooling water exert a considerable influence on the corrosion of the carbon steel pipeline connecting the pressure vessel of the reactor to the turbine and the condenser. In this connection, it has been proposed to control the concentration of oxygen in the water passed through the pipeline. For example, U.S. Pat. No. 3,663,725 to Wesley L. Pearl discloses such a technique that oxygen is put into the boiler feedwater to control the concentration of oxygen in the feedwater. Japanese Patent Kokai (Laid-Open) Publication No. 22994/76 to Katsumi OHSUMI discloses a technique in which drain in a feedwater heater is fed into water to be returned to the reactor pressure vessel from a condenser to control the concentration of oxygen dissolved in the water. Japanese Patent Kokai (Laid-Open) Publication No. 85696/77 to Kozo DOMON et al discloses a technique of controlling concentration of oxygen dissolved in water in a pipeline connecting condenser and a reactor pressure vessel, prior to the start of a nuclear reactor. However, heretofore, no consideration has been given to the concentration of oxygen in a cooling water retained in a pressure vessel of a nuclear reactor.
When a boiling water reactor is in operation, oxygen concentration in a cooling water or a reactor water in the pressure vessel is kept as low as 0.2 ppm. However, after the reactor is shut-down and opened to the atmosphere, oxygen in the open air is dissolved into the cooling water so that the oxygen concentration in the cooling water will increase to a saturation value, of about 7-8 ppm. Heretofore, the operation of the reactor has been started in this state and the cooling water is heated by nuclear reaction to a high level before the oxygen concentration in the cooling water is satisfactorily decreased. The cooling water with high temperature and high oxygen concentration tends to cause corrosions in core materials and/or in cooling water recirculation systems. Particularly, in case where austenite stainless steel is used in the core materials or in the cooling water recirculation systems, the austenite stainless steel tends to suffer from stress corrosion cracking.
Further, at the time of the start of nuclear reaction in the reactor, hydrogen peroxide is generated due to radioactive decomposition of water. As a result, the concentrations of oxygen and hydrogen peroxide are temporarily increased in the reactor water, thereby further deteriorating the corrosive environment.